Step-Down Controllers with

Synchronous Rectifier for CPU Power

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3

Note 1: Since the reference uses VL as its supply, V+ line-regulation error is insignificant.

Note 2: At very low input voltages, quiescent supply current may increase due to excess PNP base current in the VL linear

regulator. This occurs only if V+ falls below the preset VL regulation point (5V nominal). See the Quiescent Supply Current

vs. Supply Voltage graph in the Typical Operating Characteristics.

ELECTRICAL CHARACTERISTICS (continued)

SECFB, 0V or 4V

SHDN, 0V or 30V

SHDN, SKIP

SYNC

SYNC = 0V or 5V

No external load (Note 1)

SYNC = REF

Guaranteed by design

CSH = CSL = 6V

V+ = 4V, CSL = 0V (Note 2)

SYNC = 0V or 5V

SHDN = 0V, V+ = 30V,

CSL = 0V or 6V

Falling edge

SYNC = REF

SHDN = 0V, CSL = 6V, V+ = 0V or 30V, VL = 0V

CONDITIONS

0.1

MAX79_C

µA

2.0

MAX79_E/M

Input Current

2.0

V

VL - 0.5

Input High Voltage

%

93

96

89

91

Maximum Duty Cycle

kHz

190

340

Oscillator Sync Range

ns

200

SYNC Rise/Fall Time

ns

200

SYNC Low Pulse Width

ns

200

SYNC High Pulse Width

125

150

175

kHz

270

300

330

Oscillator Frequency

2.45

2.55

V

2.46

2.505

2.54

Reference Output Voltage

mW

4.8

6.6

Quiescent Power Consumption

mW

48

Dropout Power Consumption

15

µA

13

V+ Shutdown Current

V

1.8

2.3

Reference Fault Lockout Voltage

mV

50

Reference Load Regulation

µA

0.1

1

CSL Shutdown Leakage Current

UNITS

MIN

TYP

MAX

PARAMETER

MAX79_C

MAX79_E/M

MAX79_C

MAX79_E/M

FB = CSH = CSL = 6V,

VL switched over to CSL

15

µA

13

V+ Off-State Leakage Current

DL forced to 2V

FB, FB = REF

CSH, CSL, CSH = CSL = 6V, device not shut down

SYNC, SKIP

A

1

DL Sink/Source Current

±100

50

1.0

SHDN, SKIP

SYNC

0.5

V

0.8

Input Low Voltage

DH forced to 2V, BST-LX = 4.5V

A

1

DH Sink/Source Current

High or low, BST-LX = 4.5V

High or low

Ω

7

DH On-Resistance

Ω

7

DL On-Resistance

OSCILLATOR AND INPUTS/OUTPUTS

nA